1,546 research outputs found
Coulomb gap in the quantum Hall insulator
We calculate numerically the spectrum of disordered electrons in the lowest
Landau level at filling factor 1/5 using the self-consistent Hartree-Fock
approximation for systems containing up to 400 flux quanta. Special attention
is paid to the correct treatment of the q=0 component of the Coulomb
interaction. For sufficiently strong disorder, the system is an insulator at
this filling factor. We observe numerically a Coulomb gap in the
single-particle density of states (DOS). The DOS agrees quantitatively with the
predictions for classical point charges.Comment: 4 pages, to appear in ``Proceedings of the Tenth International
Conference on Recent Progress in Many-Body Theories'', Seattle, Sep. 10 - 15,
199
Optimal Sizing of Voltage Control Devices for Distribution Circuit with Intermittent Load
We consider joint control of a switchable capacitor and a D-STATCOM for
voltage regulation in a distribution circuit with intermittent load. The
control problem is formulated as a two-timescale optimal power flow problem
with chance constraints, which minimizes power loss while limiting the
probability of voltage violations due to fast changes in load. The control
problem forms the basis of an optimization problem which determines the sizes
of the control devices by minimizing sum of the expected power loss cost and
the capital cost. We develop computationally efficient heuristics to solve the
optimal sizing problem and implement real-time control. Numerical experiments
on a circuit with high-performance computing (HPC) load show that the proposed
sizing and control schemes significantly improve the reliability of voltage
regulation on the expense of only a moderate increase in cost.Comment: 10 pages, 7 figures, submitted to HICSS'1
Message Passing for Integrating and Assessing Renewable Generation in a Redundant Power Grid
A simplified model of a redundant power grid is used to study integration of
fluctuating renewable generation. The grid consists of large number of
generator and consumer nodes. The net power consumption is determined by the
difference between the gross consumption and the level of renewable generation.
The gross consumption is drawn from a narrow distribution representing the
predictability of aggregated loads, and we consider two different distributions
representing wind and solar resources. Each generator is connected to D
consumers, and redundancy is built in by connecting R of these consumers to
other generators. The lines are switchable so that at any instance each
consumer is connected to a single generator. We explore the capacity of the
renewable generation by determining the level of "firm" generation capacity
that can be displaced for different levels of redundancy R. We also develop
message-passing control algorithm for finding switch settings where no
generator is overloaded.Comment: 10 pages, accepted for HICSS-4
Optimal Control of Transient Flow in Natural Gas Networks
We outline a new control system model for the distributed dynamics of
compressible gas flow through large-scale pipeline networks with time-varying
injections, withdrawals, and control actions of compressors and regulators. The
gas dynamics PDE equations over the pipelines, together with boundary
conditions at junctions, are reduced using lumped elements to a sparse
nonlinear ODE system expressed in vector-matrix form using graph theoretic
notation. This system, which we call the reduced network flow (RNF) model, is a
consistent discretization of the PDE equations for gas flow. The RNF forms the
dynamic constraints for optimal control problems for pipeline systems with
known time-varying withdrawals and injections and gas pressure limits
throughout the network. The objectives include economic transient compression
(ETC) and minimum load shedding (MLS), which involve minimizing compression
costs or, if that is infeasible, minimizing the unfulfilled deliveries,
respectively. These continuous functional optimization problems are
approximated using the Legendre-Gauss-Lobatto (LGL) pseudospectral collocation
scheme to yield a family of nonlinear programs, whose solutions approach the
optima with finer discretization. Simulation and optimization of time-varying
scenarios on an example natural gas transmission network demonstrate the gains
in security and efficiency over methods that assume steady-state behavior
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